title: The stability of teletherapy-beam symmetry with gantry angle.
abstract: The authors describe a rapid means of evaluating the stability of beam symmetry as the gantry angle is varied. Two radiation detectors, a ratio circuit, and an X-Y recorder are used. The teletherapy machine is operated in the rotational mode, and the ionization-current ratio is recorded as a function of the gantry angle. This test can provide an early warning of beam-symmetry instabilities.
mesh_terms: D010315:Particle Accelerators / Q000295:instrumentation*; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000592:standards; D013679:Technology, Radiologic